Teletypewriter system



March 3, we. 3, A, KRE EK 2,@32,421

TELETYPEWRITER SYSTEM Filed NOV. 1, 1934 5 Sheets-Sheet l CENTRAL OFF/CE m4 ranfs -42 ms/rm/v EQUIPMEM' POLAR/ZED SUB. STAT/0N Arrows/5P J QkM Filed Nov. 1, 1954 s Sheets-Sheet 2 w E we" K w J VI 5 A vww m 0 awfimfici .l .L act-mm m AT TORNEV 5 shets-sheet :5

INVENTOR J. A. KRECEK TELETYPEWRITER SYSTEM Filed. Nov. 1, 1954 J. A. KRECEK VNw March 3, 1936.

ATTORNEY March 3, 1936. J. A. KRECEK TELETYPEWRITER SYSTEM 5 Sheets-Sheet 4 Filed Nov. 1, 1934 .lNl/ENTOR J. A. KREC'EK ATTORNEY Patented Mar. 3, 1936 UNITED STATES PATENT OFFICE TELETYPEWRITER SYSTEM Application November 1, 1934, Serial No. 750,922

17 Claims. (01. 1782) This invention concerns improvements in normally open loop teletypewriter circuits. These improvements relate principally to means for reducing trouble caused by differences in ground potential.

In normally open loop teletypewriter circuits, much trouble is experienced because of differences in ground potential. This trouble occurs chiefly with various signaling arrangements, such as call, recall, and answer signaling arrangements. It is also quite objectionable in that it sometimes causes faulty or unintentional operation of instrumentalities for starting unattended motors because, in many normally open loop systems, the teletypewriter motor in an unattended station is designed to be started when the operator at a central office closes and applies current to the line. In exceptional cases, differences in ground potential might originate enough current to start the motor at an unattended station. This, of course, is objectionable in that it results in needless use of the local power supply and the teletypewriter motor at an unattended station.

Accordingly, one object of this invention is to reduce trouble caused by differences in ground potential by so arranging teletypewriter circuits that the grounds will all be located at one station, namely the central ofiice.

Another object of this invention is to provide an improved arrangement for enabling a subscriber to send a break signal without encountering trouble caused by differences in ground potential and without giving a recall signal to the central ofiice operator at the same time.

Still another object of this invention is to provide an improved calling arrangement for enabling an operator to call a subscriber.

A further object of this invention is to provide an improved arrangement for enabling an operator to start a teletypewriter motor at an unattended station.

In accordance with this invention, when a subscriber wishes to transmit a recall signal, he momentarily opens the line thereby causing a relay at the central office to release. In releasing, this relay puts ground upon a circuit for momentarily lighting a lamp at the central office thereby attracting the attention of the operator. When a subscriber wishes to transmit a break signal, he does so by operating a key which shunts a resistance into the line. This resistance reduces the line current to an amount small enough to effect a break signal but large enoughto prevent a recall signal being given the operator.

A modification of the invention enables a-central office operator to call a subscriber by closing the loop and applying positive current to the line thereby causing a direct current polarized bell at the subscribers station to ring. This modification also enables an operator to start the motor at an unattended station by applying negative current to the line Whereas another modification of the invention enables an operator to start an unattended motor by applying positive current to the line.

These and other features of the invention will be described in detail in connection with the drawings in which:

Fig. 1 represents the preferred embodiment of the invention;

Fig. 2 illustrates a modification of the circuit shown in Fig. 1;

Fig. 3 shows another form of the invention which employs positive current for starting the motor of an unattended station;

Fig. 4 represents an alternative form of the invention which uses negative current for starting the motor of an unattended station; and,

Fig. 5 illustrates still another modification of the invention.

Fig. 1 shows a normally open teletypewriter circuit extending from subscribers station A to central office B and then to central office C and subscribers station D. Central office C and subscribers station D have both been represented by rectangles because they are similar respectively to central office B and subscribers station -A which have been shown in detail. In this circuit all the relays are normally in a non-operated C011.- dition and no instrumentalities are operated until either an operator or a subscriber originates a call. The teletypewriter of the subscriber at station A may be connected to the teletypewriter equipment 42 of the operator at central oflice B or of the operator at central ofiice C. Also, it may be connected to the teletypewriter of the subscriber at station D. It is to be understood, of course, that this number of stations and ofiices has been shown simply to illustrate the invention whereas in actual practice there may be several central offices each of which may be associated with many subscribers stations. Furthermore, there might be only one central office having several subscribers stations associated therewith and adapted to be interconnected for mutual communication.

If the operator at central office B wishes to call a subscriber, such as the subscriberat station'A, the operator will insert plug I into jack 2. This closes a circuit for negative current from above.

- or answer key 36.

battery 3 to pass through the sleeve contacts of plug I and jack 2, through relay 4, and then to ground thereby operating relay 4. When relay 4 operates in response to negative current from battery 3, its top armature closes the ringing circuit from the ring contacts of plug I and jack 2, over the top armature and contact of relay 4, line conductor 5, armature and contact of nonoperated relay 6, condenser 1, ringer 8, and then to ground.

The inner bottom armature of relay 4 also close at this time but performs no useful function. The outer bottom armature of relay 4 operates and closes a path for negative current from battery 9 to pass through lamp I0, key II, tip contacts of plug I and jack 2, outer bottom armature of relay 4, through relay I2, bottom contact and armature of slow-to-release' supervisory relay I3, and then to ground. The closing of this last mentioned circuit causes lamp II] to be lit as an indication to the operator at central ofiice B that the station equipment at station A isnot yet cut-in. Relay I2 does not operate at this time because it is polarized so as to operate I on positive current and not on negativecurrent.

To call the subscriber at station A, the operator at central ofiice B momentarily operates key I4 Which causes alternating current from generator I5 to be applied to the ringing circuit described This ringing current will cause ringer 8 to be intermittently operated.

If the subscriber is present at station A and wishes to answer the operators call, the subscriber can do so by momentarily closing his call This closes a path through alternating current relay I1 and a source I8 of alternating current thereby energizing relay I1. Upon being thus energized, relay I1 operates both its armatures and locks-up through its bottom armature. At the same time, an energizing path is' closed for operating the subscribers teletypewriter motor I9 from source I 8, through motor I9, top armature of operated relay I1, and then back to source I8. Motor stop contacts 20 are opened by an upward thrust of stunt bar 22 in response to the reception by station A of a preassigned stop signal, such as upper case H, transmitted over the line from central office B. When relay I1 operates, an energizing path is also closed for operating motor-generator 23 from source I8 through the top armature of relay I1, motor-generator 23, and then back to source I8. When motor-generator 23 is operated, it generates direct current which supplies biasing current to the bottom winding of line relay 28 and tends to maintain the armature of relay 28 in the position shown in the drawings. Direct current from motor-generator 23 also operates relay 6 which closes both its armatures thereby closing the normally open line circuit. The line circuit will now lead from line conductor 5, over the top armature and contact of relay 6, through line relay 28, sending contacts 24, break key 25, recall key 26, bottom contact and armature of relay 6, back to central office B over line conductor 21, armature and contact of non-operated relay I 2, through relay 29, battery 30, and then to ground. Since key I4 was only operated momentarily, when it is restored to the position shown in the drawings, positive current from battery 50 will be applied to the line circuit and will operaterelay 29.

The operation of relay 29 closes apath from ground, through its armature and contact, through slow-to-release'relay I 3, battery 3I,and

then to ground. This results in the operation of relay I3 which closes its armature thereby removing ground from the energizing circuit for lamp III. This causes lamp I0 to be extinguished thus indicating to the operator at central ofiice B that the subscriber at station A has cut-in his teletypewriter and that communication may now take place. Relay I3 is of the slow-to-release type in order to hold over during the transmission of printer signals, otherwise the lamp I0 might be unintentionally lit.

The subscriber at station A can recall the operator at central oflice B by momentarily opening his recall key 26 while relay 6 is operated and the line is closed. Operation of recall key 26 opens one side of the line; namely, the side including line conductor 21. This opens the energizing circuit for relay 29 and causes it to become non-operated. When relay 29 releases its armature, it opens the energizing circuit to relay I3 and causes it to become non-operated and to release its armature after a certain time delay. The release of the armature of relay I3 puts ground upon the energizing circuit for lamp III. This causes lamp III to light and to give a recall signal to the operator who then comes in on the circuit with her teletypewriter and communicates with the subscriber at station'A. When the subscriber closes recall key 26, relay 29 and relay I3 become operated again and lamp I0 is extinguished.

In case station A is unattended, there will be no response to the operators ring. In this event,

if the operator wishes to leave a message on.

the subscribers teletypewriter, she may do so by starting the motor I9 of the unattended teletypewriter. To do this, key I I is operated, thereby closing a circuit for positive current from battery 32 to pass through key II, tip contacts of plug I and jack 2, lower bottom armature of operated relay 4, relay I2, contact and armature of non-operated relay I3, and. then to ground. Since relay I2 is polarized to operate on positive current, it now operates. A path is now closed from alternator 33, through the top contact and armature of relay I 2, over line conductor 21, bottom armature and lowest contact of non-operated relay 6, condenser 34, alternating current relay 35, and then to ground. This serves to energize relay 35 which then operates its armature. The operation of the armature of relay 35 has the same effect as the closing of key 36; namely, it closes a circuit for connecting source I8 of alternating current to the teletypewriter motor I9 thereby starting motor I9 and motorgenerator 23. Significant current variations transmitted from central oflice B out over the line will actuate relay 28 which, in turn, will actuate receiving relay 4| at station A and communication can thus be had.

After termination of this communication, the operator at central oflice B may stop the motor I9 of the teletypewriter at station A and also disconnect the source I8 of alternating current. To do this, the operator transmits a presassigned signal, such as upper case H. This causes an upward thrust of stunt bar 22 thereby opening motor stop contacts 20. This opens the locking up circuit for relay I1 which then becomes nonoperated with the result that the path from source I8 to motor I9 is'opened. Consequently, motor I9 stops and stays stopped until relay' I1 is energized again. The operator then withdraws plug I from jack 2 thereby causing the release of relay 4. The line is thus restored to its nor- As a result, lamp ID will be lit.

mally open condition with all relays non-operated. When the subscriber at station A desires to call the operator at central ofiice B, he may do so by momentarily operating his call or answer key 36. This closes a path for alternating current from source I8 to operaterelay l1. Relay l'l locks-up in the manner described above and connects alternating current from source I 8 to motorgenerator 23 and to the teletypewriter motor l9 thereby starting both motor-generator 23 and teletypewriter motor [9. Relay 6 will be operated by direct current from motor-generator 23 as described above. This closes a circuit for positive current from battery 31 to pass through the top released armature of relay 4, over line conductor 5, top armature of operated relay 3, upper winding of relay 28, sending contacts 24, break key 25, recall key 26, bottom armature of relay 6, line conductor 21, released armature oi relay l2, through relay 29, battery 39 and then to ground.

Relay 29 is thus energized and operates its armature to close a circuit from battery 3 I, through relay I3, and then to ground. As a result, relay I3 becomes operated and closes a path from ground, through its armature, upper bottom contact and armature of non-operated relay 4, through relay 38, battery 39, and then to ground. This energizes relay 38 which operates its arma- I ture and closes a path from battery 39, armature and contact of relay 38, through line lamp 40 in the switchboard, and then to ground. Line lamp 4!) becomes lit as a result and serves to indicate to the operator at central oifice B that communication is desired.

The operator at central office B, in answering the call, will insert plug l in jack 2. This will close a path for negative current from battery 3 to pass through the sleeve of plug l to energize relay 4 as has been described above. Relay 4 will now operate its armatures and thereby open the path through its bottom armature for energizing relay 38. This will cause the release of relay 38 and its armature will open the energizing circuit for line lamp 4!! with the result that lamp 49 will become extinguished. Communication can now take place as described above.

If the subscriber at station A wishes to discontinue communication with the operator at central ofiice B, he can transmit a disconnect signal by opening his local stop key 2|, which causes relay l! to release thereby disconnecting the source l8 of power supply and causing motor l9 to stop running. Motor-generator 23 also stops thereby causing relay 6 to release. Relay 6, in releasing, opens the energizing circuit for re lay 29 and causes it to release. When the armature of relay 29 is released, it opens the energizing circuit for relay l3 causing relay l3 to release also. The release of the armature of relay I3 closes a circuit from ground, armature of relay l3, through the winding of relay l 2, lowest bottom armature of operated relay 4, jack 2, tip of plug I, key I l, lamp H], battery 9, and then to ground. This disconnect signal can be distinguished from a recall signal because a recall signal causes only a momentary lighting of lamp I3, whereas a disconnect signal causes lamp I 0 to be lit until the operator removes plug- I from jack 2.

In case the subscriber at station A has his teletypewriter connected to that of the subscriber at station D and wishes to transmit a break signal to the subscriber at station D, he may do so by opening his break key 25. The

opening of break key 25 removes the shunt across resistance 43. Resistance 43 is high enough to decrease the line current in the upper winding of polarized relay 6| sufficiently to enable the current in its lower winding to move its armature to its right contact. This applies negative current from battery 62 to the line leading to central office C and subscribers station D. However this line already has negative current applied to its other end at central oflice C by a battery comparable to battery 39 at central office 13. The negative current from these two batteries equals and opposes each other thus preventing any current from flowing in that line. This, in effect, is equivalent to an opening of that line and causes the teletypewriter at subscribers station D to become inoperative thereby indicating to the subscriber at station D that the subscriber at station A desires to interrupt him.

At the same time, resistance 43 leaves the current in the line from station A to central oince B sufficiently large to maintain relay 29 operated. This in turn, maintains relay l3 operated and prevents lamp Hi from lighting. In other words, it prevents a recall signal from being unintentionally given to the operator at central oflice B.

Fig. 2 shows a circuit which is somewhat similar to the circuit shown in Fig. 1. One point of difference is that central office B of Fig. 2 includes a polarized relay 244 for facilitating the reception of a break signal transmitted from a distant station, such as subscribers station D. This modification of the invention enables a break signal to be given the subscriber at station A without unintentionally giving a recall signal to either'the operator at central office B or C.

When the subscriber at station D transmits a break signal, he does so in the manner described for Fig, 1. That is, he operates a break key comparable to break key 225 which removes the shunt from a resistance similar to resistance 243. This resistance is large enough to decrease the line current in the upper winding of a polarized relay at central ofiice C, similar to polarized relay 233, sufficiently to enable the current in its lower winding to move its armature. to its bottom contact. This applies negative current from a battery like battery 262 to the line leading to central oifice l3 and subscribers station A. However, this line already has negative current applied to its other end at central oince B by battery 233 at central oflice B. The negative current from these two batteries equals and opposes each other thus preventing any current from flowing in that line. This, in effect, is equivalent to an opening of that line and causes the teletypewriter at the subscribers station A to become inoperative thereby indicating to the subscriber at station A that the subscriber at station D desires to interrupt him.

This causes relay 229 torelease its armature and open the energizing circuit to supervisory relay 2i 3. Because relay 2:3 is of the slow-torelease type, relay 2i3 does not immediately release, but remains operated for a certain time delay. As soon as relay 229 releases, its armature closes a path from ground, through polarized relay 244, armature of operated relay 2l3, line conductor 295, and then in parallel to battery 250 and battery 239. The reduced amount of negative current from battery 23%) which is left in the line, although too small to reoperate relay 229 is large enough to operate relay 244. Relay 244, in operating, closes a path from ground,

through its armature, relay 2|3, battery 23!, and

mains closed.

Thus,by means of relay 244 maintaining closed an energizing path for relay 213, relay 213 keeps its armatures operated. As long as the bottom armature of relay 2 [3 remains operated, the path for lighting supervisory lamp 2|0 will be open; On the other hand, if it were not for relay 244 keeping relay 2 I3 energized, relay 2l3 would now release its armatures, the bottom one of which would close the energizing path for lamp 2H1. This would light lamp 2H) and cause the operator to come in on the circuit with her position equipment 242. Since she is not wanted at this time, this would be an annoyance to the-subscribers. This is obviated by this modification of the invention which, as just described, enables a break signal to be given the subscriber at station A without unintentionally giving a recall signal to either the operator at central office B or C.

Fig. 3 illustrates a system which operates in a manner quite similar to that shown in Fig. 1 except that it employs a different method for enabling an operator at a central oflice to start the teletypewriter motor at an unattended subscribers station.

It can be seen in Fig. 3 that, in the normally unoperated condition of the circuit, negative current from battery 34! will pass through the armature of non-operated polarized relay 3 I 2, over line conductor 321, through the bottom armature of non-operated relay 305, polarized relay 345 and. then to ground. However, relay 345 is so polarized as to operate on positive current but not on negative current. Therefore, under the above conditions, it will remain non-operated.

I When an operator at a central office, such as central office B1, wishes to start the teletypewriter motor of an unattended subscribers station, such as station A1, she does so by first inserting plug 30! in jack 302. This closes a path for negative current from battery 303 to operate relay 304 as described for Fig. l. The operator then momentarily operates key 3i l to its upper position thereby closing a path for positive current from battery 332 to pass through key 3! tip contacts of plug'30l,'and jack 302, relay 3%2, bottom armature and contact of operated relay 304, armature of non-operated relay 3|3, and then to ground. Since relay 3l2 is polarized to operate only on positive current, it now operates its armature.

This applies positive current from battery. 346 to line conductor 327 instead of negative current from battery 341. The positive current from battery 340 will energize polarized relay 345 and cause it to operate its armature. The operation of the armature of relay 345 has the same effect as the closing of key 336; namely, it closes a circuit for connecting source 3i0 of alternating current to the teletypewriter motor 3|9 thereby starting motor 3l9. At the same time, it connects source 3! to motor generator 323 thereby supplying direct current to operate relay 306 which closes the normally open line. Communication may now take place.

Inthe circuit shown in Fig. 4, the functioning is similar to that described for the circuit shown in Fig. 1 except that a direct current bell 449, polarized so as to operate only on positive current, is used for calling a subscriber and an unattended start is made by applying negative current to the lay 406 to operate its armatures.

line. There are also a few other differences that will appear from the following description.

The operator at a central ofiice, such as central office B", can call a subscriber at a station, such as station A, by inserting plug 40l into jack 402. This connects negative current from battery 403 to relay 404 with the result that relay 404 operates its four armatures. middle bottom armature of relay 404 closes a path from battery 400, through lamp 4l0, tip contacts of plug MI and jack 402, middle armature of operated relay 404, armature of non-operated relay 4 l3, and then to ground. This causes lamp 4) to light. Lamp 4!!) is extinguished when the subscriber answers the operators call as will be explained subsequently.

The closing of the top armature of relay 404 closes a path for positive current from battery 450 to pass through the operators position equipment 442, over key 414, ring contacts of plug 40! and jack 402, top armature of operated relay 404, out over line conductor 405 to station A", top armature of non-operated relay 400, through polarized direct current bell 449, through relay 445, and then to ground. Since bell 449 is polarized so as to operate on positive current but not on negative current, it now operates and calls the subscriber at station A". Relay 445 is polarized to operate on negative current, but not on positive current. Consequently, relay 445 does not operate at this time. In case a steady ring of bell 449 is not desired, battery 450 may be intermittently applied to the ring lead in the cord circuit by any well-known means.

The subscriber answers the operators call by momentarily closing his call or answer key 436. This closes a path which enables alternating current from source M8 to operate alternating current relay 4| 1 which locks-up through its bottom armature. Relay 411, in operating, connects the power supply source 4 I 8 to the teletypewriter motor M9 and, at the same time, connects the power supply source M8 to motor generator 423. Direct current from motor generator 423 will cause re- This closes a path from ground through battery 450, key 4, plug 40I, jack 402, top armature of operated relay 404, line conductor 405, top armature of operated relay 405, line relay 423, sending contacts 424, break key 425, recall key 426, bottom armature of operated relay 406, line conductor 421, relay 429, battery 430 and then to ground. As a result, relay 429 will operate its armatures.

This closes a path from battery 43I through relay M3 and then to ground. Consequently, relay 4 I 3 will now operate its armature. This opens the path from battery 409, through lamp 410, plug 40l, jack 402, middle bottom armature oi operated relay 404 to the ground connected to the armature of relay 4I3. With ground removed from this energizing circuit for lamp 4l0, lamp 4 l 0 will now be extinguished thereby indicating to the operator at central office B that the subscriber at station A has answered. Relay 413 is of the slow-to-release type so that it will not be unintentionally released by accidental openings of the line and also so that it will hold over The closing of the.

she can do so in the following manner. First, she must insert plug 40! in jack 402 in order to enable current from battery 463 to operate relay 404. Then she moves key M4 to its lower position. This sends negative current from battery 448 out over line conductor 405, through polarized bell 449, through polarized relay 445 and then to ground. Since bell 443 is polarized to operate on positive current but not on negative current, it will not be operated now. However, since relay 445 is polarized so as to operate on negative current and not on positive current, it will operate now. The closing of the armature of relay 445 has the same effect as the closing of key 436. Consequently, the teletypewriter motor M9 and motor-generator 423 will now be operated. Relay 406 will operate and connect the line to the printer equipment for communication purposes.

The station equipment may be restored to its normally unoperated condition by the transmission of a stop signal which will cause an upward thrust of stunt bar 422 thereby opening motor stop contacts 420. This opens the locking-up circuit for relay 4!! and disconnects the power supply source 4 l3 from motor '4 I 6 and motor-generator 423. This causes relay 406 to release its armatures.

The subscriber can call the operator by momentarily closing his call or answer key 436. This starts his teletypewriter motor 4!!) and motor-generator 423 in the manner described above. As a result, relay 406 will be operated, and will cut-in the station printer equipment. However, relay 456 will not be energized by direct current from motor-generator 423 until after a certain time delay required for motor-generator 423 to become operated. During this interval of time a path will be closed for current from battery 430 to pass through relay 429, over line conductor 421, bottom armature of non-operated relay 406, top set of contacts of key 436 and then to ground.

This causes relay 429 to operate its armature and to thereby close a path from battery 43! through relay 4! 3 to ground thereby operating relay 4!3. Relay 4!3, in operating, closes a path for negative current from battery 439 to pass through relay 438, upper bottom armature of non-operated relay 404, armature of operated relay M3, and then to ground. As a result, relay 438 will become energized and lock up through its left armature subject to the operation of relay 404. Its right armature will close a path for current from battery 439 to light line lamp 440 thereby indicating to the operator at the central oflice B that the subscribers station A" desires attention. By the time relay 406 becomes energized and opens the energizing path for relay 429, relay 438 will have locked up, thus maintaining lamp 440 lighted until the operator answers the call.

When the operator answers the call she will insert plug 40! in jack 402 thereby enabling current from battery 463 to operate relay 404. The operation of the lower bottom armature of relay 404 will open the locking-up circuit for relay 433 which will new release. in turn, will extinguish line lamp 440.

Recall and break signals can be transmitted in a manner similar to that described for the circuit shown in Fig. 1.

In the circuit shown in Fig. 5, the operator at a central oflice, such as central office B2, can call a subscriber at a subscribers station, such as station A2 in the following manner. First, the opera-tor'inserts plug 50! in jack 502. This closes a path for current from battery 503 topass through and operate relay 504. The operator then closes key 5! 4. The lower set of contacts of key 5|4 close a path for ringing current from alternator 5E5 to pass through plug 50! and jack 502, over the top armature of operated relay 504, out over lineconductor 56 5, to station A2, through condenser 551, ringer 550 and then to ground. The operation of ringer 558 serves to attract the attention of the subscriber.

At the same time, the upper set of contacts of key .5! 4 close a path, after relay 504 has operated, for positive current from battery 532 to pass through plug 50!, jack 552, relay 55!, middle bottom armature of operated relay 504, armature of non-operated relay 5l3, and then to ground. Since relay 55! is polarized so as to operate on positive current, but not on negative, it will operate now. Relay 55!, in operating its armature away from its contact, prevents relay 552 from being operated. Since the operation of relay 513 is dependent upon the operation of relay 552, relay 5!3 will now be non-operated.

When the operator ceases ringing, she restores key 5!4 to the position shown in the drawings, thereby establishing a path for negative current from battery 509 to travel through lamp 5N3, key 5I4, tip contacts of plug 50! and jack 502, through relay 55!, middle bottom armature of operated relay 504, armature of non-operated relay 5I3 and then to ground. Since relay 55! is polarized so as to operate on positive current, but not on negative current, it will become non-operated and will release its armature to close its contact.

At the same time, positive current from battery 550 will pass through the operators position equipment 542, high resistance 551, key '5I4, ring contacts of plug 50! and jack 502, top armature or" operated relay 504, out over line conductor 505, over the top armature of nonoperated relay 505, through resistance 555, re lay 553, bottom armature of non-operated relay 506, line conductor 521, relay 552, armature of non-operatedrelay 55!, battery 556, and then to ground. Resistances 555 and 551 are high enough to reduce the line current to an amount too small to operate either relay 553 or relay 552. If the subscriber at station A2 is present when the operator at central office B2 rings, he can answer by closing his call or answer key 536. The lower set of contacts of key 536 will connect power supply source 518 to the teletypewriter motor 5I9 and rectifier 554 in the manner described for the circuits shown in the other figures. Direct current from'rectifier 554 will now operate relay 506 which, in operating its armatures, will connect the line to the station printer equipment. Since the resistance of the printer equipment is lower than that of resistance 555, the line current will now be increased to an amount large enough to operate relay 552. Relay 552, in operating, closes a path from ground through its armature, relay 513, battery 53!, and then to ground. This enables relay 5|3 to operate its armatures thereby opening the energizing path for supervisory lamp 5I0. Consequently, lamp 5!0 becomes extinguished, thus indicating to the operator that the subscribers printer equipment has been cut into the line.

In case station A2 is unattended, the operator at central office B2 can start the teletypewriter motor 5!!! by first inserting plug 50! in jack 502. This enables current from battery 503 to operate relay 504 and to apply positive current from battery 550 to the line in the manner described above. 'The operator now closes key558 thereby short-circuiting high resistance 551. This increases the line current to an amount large enough to operate relay 553. When relay 553 closes its armature, it connects power supply source 518 to the teletypewriter motor 5l9 and rectifier 554 in the same manner as when key 536 is closed.

When the operator has finished sending the message, she sends a motor-stop signal which operates stunt bar 522 thereby opening motorstop contacts 520. This opens the energizing circuit for motor 5!!! and motor generator 554 and causes them to release.

The subscriber at station A2 can call the operator at the central oflice B2 by momentarily operating his call or answer key 536. The upper contacts of key 536 supply ground to the path leading from battery 556, through the armature of non-operated relay 55L to relay 552. This operates relay 552 which closes a path for operatlng relay 5! 3 as described above. Relay 513 then closes a path from ground through its right armature, upper bottom armature of non-operatedv relay 504, relay 559, battery 560, and then to ground. This causes relay 559 to operate and to lock-up through its left contact, armature of non-operated r'elay 504, and then to ground. This locking-up circuit is opened when relay 504 is operated. At the same time, an energizing path is closed from battery 560, right armature of operated relay 559, lamp 540 and then to ground thereby lighting lamp 540. This serves to attract the attention of the operator at central oflice B2 and to indicate to her that the subscriber at station A2 desires attention.

4 When key 536 is operated, its lower contacts connect power supply source 5|8 to teletypewriter motor SH! and rectifier 554. Although key 536 is operated only momentarily, relay 5" looks up through its lower contact and armature and maintains the connection of power supply 5I 8 to motor 5l9 and rectifier 554. Direct current from rectifier 554 will operate relay 506 thereby connecting the line to the station printer equipment. This opens the energizing circuit for relay 552 and causes it to release. The release of relay 552 causes the release of relay 5l3. However, lamp 540 is not extinguished at this time because relay 559 is locked up by a path through its left armature and over the lower bottom armature of relay 504. 7

When the operator at central oflice B2 answers the call from the subscriber at station A2, she inserts plug 50l into jack 502 thereby closing a path for operating relay 504. Relay 504, in operating its lower bottom armature, opens the locking-up circuit for relay 559. Consequently, relay 559 releases and opens the energizing circuit for lamp 540 thereby extinguishing lamp540.

Break and recall signals may be transmitted 1 in amanner similar to that described in the circuit shown in Fig. 2.

The above circuits have been shown and described in order to illustrate the principles of this invention. It should be understood that different arrangements employing the principles and fea What is claimed is:

Y 1. A teletypewriter system having two teletypewriter stations, a telegraph line extending from one stationto the other, a source of line current located at only one station and adapted to be applied to the line, and instrumentalities for reducing trouble caused by differences in ground potential, said instrumentalities including circuit means for grounding the source of line current at only the station at which it is located.

2. A teletypewriter system having two teletypewriter stations, a telegraph line extending from one station to the other, a source of signal current at one station, a ground connection at the same station for the source of signal current, said ground connection being normally disconnected from the source of signal current, and 1nstrumentalities for connecting the ground to the source of signal current.

3. A teletypewriter system having two teletype Writer stations, a telegraph line extending from one station to the other, a source of signal current at one station, a ground connection at the same station for the source of signal current, said ground connection being normally disconnected from the source of signal current, and instrumentalities for connecting the ground to the source of signal current, said instrumentalities being located at the other station and being capable of being actuated from either station.

' 4. A teletypewriter system having two teletypewriter stations, a telegraph line extending from one station to the other, the first of said stations having a teletypewriter motor and a source of power supply for operating the motor, said source being normally disconnected from the motor, and instrumentalities for enabling the operator at the second station to start the motor by connecting the source of power supply to the motor, said instrumentalities including an electro-responsive device located at the first station, said device being responsive to alternating current, a source of alternating current at the second station, and control means at the second station for applying the source of alternating current to the electro-responsive device, said control means operating only on positive current.

5. A teletypewriter system having two teletypewriter stations, a telegraph line extending from one station to the other, a source of line current at only one station and adapted to be applied to the line, circuit means for grounding the line current at only the station at which it is located, recall instrumentalities for momentarily opening the line for giving a recall signal, break instrumentalities for reducing the signal current to an amount small enough to effect a break signal, but large enough to maintain the line closed for preventing a recall signal from being unintentionally efiected.

' 6. A teletypewriter system having a central teletypewriter office, a subscribers teletypewriter station, a normally open telegraph line extending from the subscribers station to the central office, a source of signal current at the central office, a ground connection at the central ofilce for the source of signal current, said ground connection being normally disconnected from the source of signal current, control instrumentalities at the central oflice and the subscribers station for closing the normally open line and for connecting the ground connection tothe source of signal current, recall instrumentalities at the subscriber's station for disconnecting the ground connection (after the control instrumentalities have connected it to the source of signal current) from the source of signal current and for causing an indication of this to be given to the operator at the central office, a resistance at the subscribers station, and break instrumentalities at the subscribers station for shunting the resistance into the line (after the control instrumentalities have closed the line) for reducing the line current to an amount small enough to effect a break signal but large enough to prevent a recall signal from being given the central oflice operator at the same time.

7. A teletypewriter system having a central teletypewriter oilice, a subscribers teletypewriter station, a normally open telegraph line extending from the subscribers station to the central ofi'ice, a source of signal current at the central office, a ground connection at the central office for the source of signal current, said ground connection being normally disconnected from the source of signal current, control instrumentalities at the subscribers station for closing the normally open line and for connecting the ground connection to the source of signal current for communication purposes, recall instrumentalities at the subscribers station for enabling the subscriber to momentarily disconnect the ground connection from the source of signal current (after the control instrumentalities have connected it to the source of signal current for communication purposes) and for causing an indication of this to be given to the operator at the central ofiice, a resistance at the subscribers station, and break instrumentalities at the subscribers station for shunting the resistance into the line (after the control instrumentalities have closed the line for communication purposes) for reducing the line current to an amount small enough to eiiect a break signal but large enough to operate instrumentalities at the central office for preventing a recall signal from being given the central office operator, said instrumentalities including a polarized relay located at the central office.

8. A teletypewriter system having two teletypewriter stations, a telegraph line extending from one station to the other, a. source of line current at one station and adapted to be applied to the line, circuit means for grounding the line current at only the station at which it is located, recall instrumentalities for momentarily opening the line for giving a recall signal, break instrumentalities for reducing the signal current to an amount small enough to efiect a break signal but large enough to maintain the line closed for preventing a recall signal from being unintentionally eifected, said break instrumentalities including a polarized relay.

9. A teletypewriter system having two teletypewriter stations, a telegraph line extending from one station to the other, the first of said stations having a teletypewriter motor and a source of power supply for operating the motor, said source being normally disconnected from the motor, and instrumentalities for enabling an operator at the second station to start the motor by connecting the source of power supply to the motor, said instrumentalities including an electro-responsive device at the first station, said device being responsive to alternating current, a source of alternating current at the second station, and control means at the second station for applying the source of alternating current to the electro-responsive device, said control means being operable only by current of a preassigned polarity.

10. A teletypewriter system having two teletypewriter stations, a telegraph line extending from one station to the other, the first of said stations having a teletypewriter motor and a source of power supply for operating the motor, said source being normally disconnected from the motor, and instrumentalities for enabling an operator at the second station to start the motor by connecting the source of power supply to the motor, said instrumentalities including an electro-responsive device at the first station, said de vice being responsive to alternating current, a source of alternating current at the second station, and control means at the second station for applying the source of alternating current to the electro-responsive device, said control means having a normally open energizing circuit, actuating means for closing said energizing circuit,

and operating means for operating the actuating means, said operating means including a source of negative current.

11. A teletypewriter system having two teletypewriter stations, a normally open telegraph line extending from one station to the other, the first of the stations having a direct current polarized bell operable only by positive current, and the second of the stations having calling instrumentalities for closing the normally open line and for applying positive current to the line for operating the bell at the first station, said call ing instrumentalities including electro-magnetic means for closing the line and a source of negative current for operating said electromagnetic means.

12. A teletypewriter system having a central teletypewriter ofiice, a subscribers teletypewriter station having a teletypewriter motor, a normally open telegraph line extending from the central office to the subscribers station, control instrumentalities for closing the normally open line, and motor control means for enabling an operator at the central ofiice to start the teletypewriter motor at the subscribers station, said motor control means including a normally open energizing circuit for the motor, and a normally non-operated polarized relay located at the subscribers station and connected into the line, said energizing circuit being closed by the operation of the polarized relay, said relay being operable only by negative current, and instrumentalities located at the central ofiice for enabling an operator to apply negative current to the line for operating the polarized relay at the subscribers station to close the energizing circuit for the motor.

13. A teletypewriter system having two teletypewriter stations, a telegraph line extending from one station to the other, the first of said stations having a teletypewriter motor and a source of power supply for operating the motor, said source being normally disconnected from the motor, and motor control means for enabling an operator at the second station to start the motor by connecting the source of power supply to the motor, said means including an impedance for reducing the line current, an instru-' mentality for increasing the line current, and an electro-responsive device operable by an increase in the line current for connecting the source of power sup-ply to the motor.

14. A teletypewriter system having two teletypewriter stations, a normally open telegraph line extending from one station to the other, th

first of said stations having a teletypewriter motor and a source of power supply for operating the motor, said source being normally disconnected from the motor, and motor control means for enabling an operator at the second station to start the motor by connecting the source of power supply to the motor, said means including an impedance at each station for reducing the line current, an instrumentality at the second station for increasing the line current by short-circuiting the impedance at the second station, and an electroresponsive device at the first station operable by an increase in the line current for connecting the source of power supply to the motor.

15. A teletypewriter system having a subscrib ers teletypewriter station connectible to a teletypewriter central ofiice by a telegraph line, said subscribers station having a teletypewriter motor and a source of power supply for operating the motor but normally disconnected therefrom by the armature of an alternating current relay also located at the subscribers station and connected into the line, a source of alternatingcurrent at the central office normally disconnected from the line by the armature of a relay located at the central oflice and polarized to operate on negative current, and control means at the central ofiice for applying negative current to the polarized relay whereby the source of alternating current is connected to the, line for operating the alternating current relay to connect the subscribers power supply source to his motor.

16. A teletypewriter system having in combina tion a teletypewriter central office, a subscriber's station having teletypewriter apparatus, a telegraph line extending from the subscribers station to the central office, said telegraph line being normally disconnected from the subscriber's teletypewriter apparatus, said central office having a calling lamp with an energizing circuit which is normally open at the armature of a first relay located at the central office and normally unoperated, an energizing circuit at the central ofiice for the first relay, said energizing circuit being normally open at the armature of a second relay which has an energizing circuit which is normally open at the armature of a third relay which is normally unoperated and connected into the telegraph line, control means at the subscribers station for connecting the line to the subscribers teletypewriter apparatus and for applying current to the line to operate the third relay thereby operating the second and first relays in turn with the consequent illumination of the calling lamp.

17. A teletypewriter system having in combination a teletypewriter central oflice, a subscribers station having teletypewriter apparatus, a telegraph line extending from the subscribers station to the central ofilce, control means for connecting the line to the subscriber's teletypewriter apparatus, a disconnect lamp located at the central office and having an energizing circuit which is open during communication at the armature of a first relay, said first relay being operated by an ener gizing circuit which is closed during communication by the armature of a second relay which is operated at that time, and a control instrumentality at the subscribers station for causing the second relay to release its armature to open the energizing circuit of the first relay whereby the energizing path for the disconnect lamp is closed and the lamp illuminated.

JOSEPH A. KRECEK. 

